1985 F-150 fire in the heater / defroster. This post refers to the caller in show 1343 that had some bugs catch on fire in the heater system thus smoking up the cab. Click and Clack said there's nothing in the system that can get hot enough to do that except the blower motor (burning insulation) which must have been the problem. Au contraire...the resistor used for regulating the blower motor speed is in there too and it glows red hot sometimes and will set things on fire sometimes. (I have a couple of personal experiences that led me to this observation and conclusion. The stories are kinda funny and the truck survived - no harm no foul (except for the smell!)